The Metropolitan Police Department has issued some 7,000 speeding tickets and demanded more than $1.2 million in fines since November from speed cameras in the Third Street Tunnel in Northwest D.C.

But the tickets and the fines could be subject to legal challenge and a refund based on a technical but avoidable error, according to internal documents obtained by The Washington Times, which would be the second mistake within the D.C. police department’s Automated Traffic Enforcement Unit this year.

The posted speed limit in the tunnel, which runs from Interstate 395 to Massachusetts Avenue, ordinarily is 45 mph. But since construction to improve lighting and air exchange began in October, the posted speed limit has been 40 mph, along with signage to indicate “Work Zone,” “Fines Double” and “Photo Enforced.”

In response to a Freedom of Information Act request by The Times, the Department of Motor Vehicles disclosed recently that two speed cameras in the tunnel — facing north and south — generated 6,981 speeding tickets between November and the end of April. Fines associated with those tickets totaled $1,206,795, according to the DMV.

However, police deployment logs from December through April obtained by The Times show that while the posted speed limit in the tunnel during this time was 40 mph, the posted speed limit recorded by the department in the issuance of the citations was 45 mph.

According to Title 18 of the D.C. Municipal Regulations, the police department is required to enforce the posted speed limit, which also is known as the “absolute speed limit,” and failure to do so could invalidate the ticket or tickets — which in this case resulted in thousands of fines beginning at $125.

Lisa Sutter, a civilian who heads the automated traffic enforcement unit, referred inquiries to police spokeswoman Gwendolyn Crump. In an email Wednesday, Ms. Crump confirmed that the posted speed limit in the Third Street tunnel is usually 45 mph, and that during construction, the posted speed limit has been 40 mph.

“We have kept the photo enforcement speed limit at 45 mph,” she wrote, “since it was not clear when the construction would be finished and the D.C. Department of Transportation did not ask us to enforce at the 40 mph speed limit.”

Ms. Crump said that for speed cameras such as the ones that are in the tunnel, a technician accompanied by a sworn police officer visits each unit every day, even though the legal requirement is only every four days. The deployment log is considered evidence and is available at the hearing for the ticket.

“Any tickets issued have been issued for traveling in excess of 45 mph, not 40 mph,” she added. “Drivers should obey the posted speed limits or drive slower if conditions do not permit travel at that speed.”

In a follow-up email, Ms. Crump claimed the posted sign in the tunnel was intended for the work zone when workers are present. “There are never any workers in our enforcement zone,” she said. “We are not issuing tickets for people going faster than 40, only 45, which is the speed limit there when workers aren’t present.”

John B. Townsend II, manager of public and government affairs for AAA Mid-Atlantic, said such practices “make the motoring public highly suspicious of automated traffic programs.”

“They question the integrity of the program and wonder aloud if the District is putting profits ahead of traffic safety. Once the accuracy and integrity of the system are compromised or brought in question because things are being done with a wink or a nod or on the slipshod, the program is undermined and motorists lose confidence in law enforcement,” he said.

Mr. Townsend said the District brought in more than $55 million in automated enforcement fines last year, bolstered by an increase of fines such as the ones levied from the Third Street Tunnel of 150 percent.

This would not be the first time the police department’s automated ticket unit issued invalid speeding tickets and fines to unsuspecting motorists.

In March, WRC-TV (Channel 4) reported that the unit issued more than 100,000 speeding tickets that were in violation of National Highway Traffic Safety Administration regulations that the District adheres to in enforcing its own traffic laws.

NHTSA regulations require that when cameras are used to enforce speed limits, there must be secondary measurement to ensure accuracy, such as white painted lines on the road to show the distance a car traveled while recorded by the camera.

However, when the speed camera program began, the automated ticket unit made the decision to not include them. Photos of streets where cameras are located that both include and do not include the white painted lines, and internal police emails obtained by The Times, show the discrepancy and the subsequent decision by police officials to temporarily shut down at least six noncompliant camera sites.

While it is unclear whether the fines associated with some 100,000 speeding tickets from those sites were refunded, The Times is aware of at least one $125 refund of a ticket issued from a camera at one of the noncompliant locations, along with a written explanation that the ticket should have been processed as a warning.

It is unclear whether there are other instances in which the District offered such an explanation in refunding a speeding fine that had already been paid.

The office of D.C. Council member Phil Mendelson, at-large Democrat who chairs the Committee on Public Safety, which oversees the police department, did not respond to requests for comment.